Witch of Git - jade-rose/blob - toolchain/src/inst/decode.rs

   1 use super::{AddImm, AluI, Data, Inst, LdSt, Op1, OpI3, OpR, Reg, Special, U3};
   2 use std::io::{self, Read};
   3
   4 pub trait Decode: Sized {
   5     fn decode(reader: &mut impl Read) -> io::Result<Self>;
   6 }
   7
   8 fn reg(x: u8) -> Reg {
   9     Reg::new(x & 0x7).unwrap()
  10 }
  11
  12 fn special(x: u8) -> io::Result<Special> {
  13     match x {
  14         0b000 => Ok(Special::Data(Data::D1)),
  15         0b001 => Ok(Special::Data(Data::D2)),
  16         0b010 => Ok(Special::Code),
  17         0b011 => Err(io::Error::new(
  18             io::ErrorKind::InvalidInput,
  19             "Reserved special register",
  20         )),
  21         _ => Err(io::Error::new(
  22             io::ErrorKind::InvalidInput,
  23             "Invalid special register",
  24         )),
  25     }
  26 }
  27
  28 fn op1(x: u8) -> Op1 {
  29     match x {
  30         0b000 => Op1::Zero,
  31         0b001 => Op1::Lsl1,
  32         0b010 => Op1::Lsr1,
  33         0b011 => Op1::Asr1,
  34         0b100 => Op1::Incr,
  35         0b101 => Op1::Decr,
  36         0b110 => Op1::Comp,
  37         0b111 => Op1::Negt,
  38         _ => unreachable!(),
  39     }
  40 }
  41
  42 fn op_r(x: u8) -> OpR {
  43     match x & 7 {
  44         0b000 => OpR::Add,
  45         0b001 => OpR::Sub,
  46         0b010 => OpR::And,
  47         0b011 => OpR::Ior,
  48         0b100 => OpR::Xor,
  49         0b101 => OpR::Lsl,
  50         0b110 => OpR::Lsr,
  51         0b111 => OpR::Asr,
  52         _ => unreachable!(),
  53     }
  54 }
  55
  56 fn flag(x: u8) -> bool {
  57     x & 2 != 0
  58 }
  59
  60 fn op_compact(x: u8) -> OpI3 {
  61     match (x >> 3) & 7 {
  62         0b000 => OpI3::Rol,
  63         0b001 => OpI3::Lsl,
  64         0b010 => OpI3::Lsr,
  65         0b011 => OpI3::Asr,
  66         0b100 => OpI3::Clr,
  67         0b101 => OpI3::Ins,
  68         0b110 => OpI3::Tog,
  69         0b111 => OpI3::Ext,
  70         _ => unreachable!(),
  71     }
  72 }
  73
  74 fn ldst(o: u8) -> LdSt {
  75     if o & 0x1 == 0 {
  76         LdSt::Ld
  77     } else {
  78         LdSt::St
  79     }
  80 }
  81
  82 fn data(o: u8) -> Data {
  83     if o & 0x4 == 0 {
  84         Data::D1
  85     } else {
  86         Data::D2
  87     }
  88 }
  89
  90 impl Decode for Inst {
  91     fn decode(reader: &mut impl Read) -> io::Result<Self> {
  92         let mut op_byte = [0];
  93         reader.read_exact(&mut op_byte)?;
  94         Ok(match (op_byte[0] >> 3, op_byte[0] & 7) {
  95             (0b0000_0, 0b000) => Inst::Trap,
  96             (0b0000_0, 0b001) => Inst::Nope,
  97             (0b0000_0, 0b010) => Inst::Prnt,
  98             (0b0000_0, 0b110) => Inst::CAbA,
  99             (0b0000_0, 0b111) => Inst::COfA,
 100             (0b0000_1, o) => Inst::Alu1(op1(o)),
 101             (0b0001_0, s) => Inst::Get(special(s)?),
 102             (0b0001_1, s) => Inst::Set(special(s)?),
 103             (0b0010_0, r) => Inst::GetR(reg(r)),
 104             (0b0010_1, r) => Inst::SetR(reg(r)),
 105             (0b0011_0, r) => Inst::Swap(reg(r)),
 106             (0b0011_1, r) => Inst::IsLt(reg(r)),
 107             (o @ 0b0100_0..=0b0111_1, r) => Inst::AluR(op_r(o), reg(r)),
 108             (o @ 0b1000_0..=0b1011_1, r) => Inst::Mem(ldst(o), data(o), reg(r), flag(o)),
 109             (0b1111_0..=0b1111_1, _) => {
 110                 let mut imm_byte = [0];
 111                 reader
 112                     .read_exact(&mut imm_byte)
 113                     .map_err(|e| match e.kind() {
 114                         io::ErrorKind::UnexpectedEof => io::Error::new(
 115                             io::ErrorKind::InvalidInput,
 116                             "Extended instruction missing operand",
 117                         ),
 118                         _ => e,
 119                     })?;
 120                 let imm = imm_byte[0];
 121                 match op_byte[0] & 0xf {
 122                     0b0000 => Inst::AluI(AluI::And(imm)),
 123                     0b0001 => Inst::AluI(AluI::Ior(imm)),
 124                     0b0010 => Inst::AluI(AluI::Xor(imm)),
 125                     0b0011 => match imm >> 6 {
 126                         0b00 | 0b01 | 0b11 => {
 127                             Inst::AluI(AluI::Add(AddImm::new(imm as i8).unwrap()))
 128                         }
 129                         0b10 => {
 130                             let imm3 = U3::new(imm & 7).unwrap();
 131                             Inst::AluI(AluI::Compact(op_compact(imm), imm3))
 132                         }
 133                         _ => unreachable!(),
 134                     },
 135                     0b0100 => Inst::BEzI(imm as i8),
 136                     0b0101 => Inst::JOfI(imm as i8), /* reserved branch */
 137                     0b0110 => Inst::CAbI(imm),
 138                     0b0111 => Inst::COfI(imm as i8),
 139                     0b1110 => Inst::GetI(imm),
 140                     0b1111 => {
 141                         return Err(io::Error::new(
 142                             io::ErrorKind::InvalidInput,
 143                             "reserved extended EXT1",
 144                         ))
 145                     } /* reserved with immediate */
 146                     _ => {
 147                         return Err(io::Error::new(
 148                             io::ErrorKind::InvalidInput,
 149                             "reseved with immediate",
 150                         ))
 151                     } /* reserved with immediate */
 152                 }
 153             }
 154             _ => {
 155                 return Err(io::Error::new(
 156                     io::ErrorKind::InvalidInput,
 157                     "invalid instruction",
 158                 ))
 159             }
 160         })
 161     }
 162 }